Indicator



Jan. 30, 1945. CQXON I 2,368,289

INDICATOR Filed Dec. 29, 1941 i &9 I 66 Patented Jan. 30, 1945 INDICATOR George E. Coxon, Cicero, Ill., assignor to Stewart-Warner Corporation, Chicago, 111., a corporation of Virginia Application December 29, 1941; Serial No. 424,807

8 Claims. (Cl. 171-95) My invention pertains to indicators and more particularly to a thermal type receiver unit for an indicator of the kind commonly used on automobiles to show the oil pressure in the engine oiling system, to show the temperature of the engine cooling liquid, to show the quantity of gasoline in the main fuel tank, and for similar purposes.

An object of my invention is to' provide an indicator of the class described which is more 1 of curvature of its arc. The free length of the accurate than those now in use. strip 23 is equal to that of the strip 34 so that Another object of my invention is to provide the combined strips automatically compensate for an indicator which may be manufactured more variations in ambient temperature. quickly and economically than the indicators The pointer shaft l6 has an actuating arm 40 now in use. connected by link 42 to bracket 44 welded or Another object of my invention is to provide otherwise secured to'the free end 46 of bimetalan indicator which is of simple and rugged conlic strip 34. The actuating arm 40 is provided struction and which will provide long and trouwith stop fingers 48 and 50 and these stop finble-free service. gers are adapted to engage the bracket I2 to de- Other objects of my invention will become termine the extreme posit ons of e D 1n e apparent as the description proceeds. An actuating coil 52 is wound around the actu- In the drawing: ating bimetallic strip 26. One end of this coil Fig. 1 is a front view of an indicator embodyis connected to battery terminal 54 and the other ing one form of my invention; end to rheostat terminal 56. As clearly shown Fig. 2 is a view on an enlarged scale looking in Fi 3, t e t i 54 i ad pte to e in the same direction as Fig. 1. but with parts connected to a battery 58 or other suitable removed to show more clearly the internal consource of electrical energy W i is grounded struction; at 60.

Fig. 3 is a side elevation of the indicator of Rheostat terminal 56 is ad p o be 0 1 on an enlarged scale and showing the nected toarheostat 8| or other resistance which electrical connections diagrammatically; varies with the characteristic to be indicated and Fig. 4 is a front view of a modified form of Such otat is grounded at 6 my invention; and A voltage compensating coil 64 is wound about Fig. 5 is an enlarged view of the indicator the compensating strip 34. One end of the coil of 4 w h p rts rem ved to show the in- 64 is connected to battery terminal 54, and the ternal construction. other end of this coil is grounded to bimetallic Referring particularly to Figs. 1, 2,. and 3. it will strip 34 as indicated at 66. It will be understood be seen that I have provided an indicator reby those skilled in t e t t at e rac et l2 ceiving unit having a base i0 preferably formed is rou e e t r y the means for attaching of insulating material and adapted for mountthe instrument to the instrument board of the ing on the instrument board of an automobile automobile, or by a special ground connection. or any other suitable support. A sheet metal The operation of this form of my invention is bracket I2 is attached to the support and proas follows: In Figs. 1 and 2 the pointer is shown vides a bearing I4 for a pointer shaft l6 havr at the zero or lower end of the scale and this im: a pointer I8. position corresponds to a maximum resistance The pointer is located in juxtaposition to a of the rheostat 6| and a minimum current in dial 20 carrying suitable indicia as clearly inthe actuating coil 52. Any changes in ambient dicated in Fig. 1, it being understood. of course temperature will produce no shift in the posithat the particular indicia will vary for different tion of the pointer l8, since the arrangement of uses of the instrument. The pointer and dia the bimetallic strips 26 and 34 automatically are preferably protected by a glass face plate 22 held in place by a protectingmetal rim 24 An arcuate bimetallic strip 26 has one end 28 rigidly secured to the bracket l2, and a second end 30 welded or otherwise suitably secured to the end 32 of a second arcuate bimetallic strip 34. The bimetallic strip 26 may be referred to as the actuating strip, and has its high expansion side 36 forming the inner side of the are so that heating of the strip tends to increase the radius of curvature of this strip. The compensating bimetallic strip 34 has its high expansion side 38 on the outside of the are so that heating of this strip. tends to reduce the radius compensates for variations in ambient temperature for all positions of the pointer I 8.

Any variation in battery voltage will vary the current flowing through the coil 52 and would shift the position of the pointer I8 sothat it no longer corresponded to the characteristic to be indicated, unless some voltage compensating means is provided. Such variation in battery voltage will also vary the current in the coil 64 and the current variation in the compensating coil 64 produces a change in curvature in the bimetallic strip 34, which compensates for the change in curvature in the bimetallic strip 26, resulting from the effect of voltage variations on the current in coil 52.

When the resistance of the rheostat BI is reduced, a greater current flows through the actuating coil 52, whereby the actuating bimetallic strip 26 is heated to a higher temperature and increases its radius of curvature. This shifts the position of the pointer I8 and accurately reflects the change in the characteristic being indicated which was responsible for the change in rheostat resistance. The pointer [8 thus at all times and for all conditions of ambient temperature and battery voltage accurately indicates the true condition of the volume of gasoline in the fuel tank or other characteristic being indicated.

When the form of my invention shown in Figure 1 is first completed and tested, it can be calibrated very easily by simply bending the arm 40, bracket 44 and stop fingers 48 and 50 so that the pointer moves over the full range of the indicia for full variation in rheostat resistance. The parts to be bent for calibration purposes are pref- "erably made of a material which will permit such bending without breaking, and are sufiiciently rigid to retain their bent positions throughout the life of the indicator.

In Figs. 4 and 5 I have shown a modified form of my invention which has the advantage of providing a much greater range of pointer movement. In this form of my invention the pointer may move over a scale occupying the entire 360 of permissible pointer movement.

In this form of my invention the pointer III is mounted on a shaft 12 which is located centrally of the thermal ring 14 and is supported in a hearing in the base 16.

A pinion 18 is attached to the shaft 12 and this pinion is driven by an arcuate rack 80 on one end of a driving member 82 pivotally mounted at 84 on the base 16.

A link 86 pivotally connects one end of the driving member 82 with a bracket 88 secured to the free end of 'the thermal ring 14. This ring comprises bimetallic strips 90 and 92 arranged back to back as in the previous embodiment. An actuating coil 94 surrounds bimetallic strip 90 and a voltage compensating coil 96 surrounds bimetallic strip 92.

The construction and operation of that form of my invention shown in Figs. 4 and 5 is essentially the same as the construction and mode of operation of the previous embodiment. The principal difference resides in the mounting of the pointer shaft and the interposition of gearing between the pointer shaft and free end of the thermal ring, whereby the pointer may travel over a range of movement of 360 or any part thereof. The embodiment of Figs. 4 and 5 is likewise provided with a battery terminal 54 and a rheostat terminal 58 and is designed to be connected in an electric circuit like that diagrammatically indicated in Fig. 3.

It will be understood that my invention is not limited to the particular details illustrated and described, but may assume numerous other forms and that the scope of my invention is defined in the following claims.

I claim:

1. In an indicator of the class described, the combination of a first indicating member, a second indicating member movable relative to said first member to indicate variations in a. given characteristic, a pair of arcuate bimetallic strips, each having a high expansion side and a low expansion side, said strips being connected so that the high expansion side or one strip is on the inner side of its arc whereas the high expansion side of the other strip is on the outer side of its arc, a rigid support for one end of said connected strips, said other end of said connected strips being free to move relative to said support, a connection between the free end of said connected strips and said second member, and means for variably heating one of said strips.

2. In a device of the class described, the combination of a pair of arcuate bimetallic strips connected so that the high expansion side of one strip is on the outside of its arc and the high expansion side of the other strip is on the inside of its arc, a fixed support for one end of said connected strips, the other end of said connected strips being free to move relative to said support, means for variably heating one of said strips, and indicating means connected to the free end of said connected strips for operation thereby.

3. In a device of the class described, the combination of a pair of bimetallic strips each having a high expansion side and a low expansion side, said strips being connected sothat the high expansion side of one strip constitutes a continuation of the low expansion side of the other strip and the low expansion side of the first strip constitutes a continuation of the high expansion side of said other strip, a fixed support for one end of said connected strips, the other end of said connected strips being free to move relative to said support, an actuating heating coil for heating one of said connected strips, said actuating coil being adapted for connection to a resistance variable in response to variations in a given characteristic whereby the current in said coil varies with said characteristic, a voltage compensating heating coil for the other strip, and indicating means connected to the free end of said connected strips.

4. In an indicator of the class described, the combination or a first indicating member, a second indicating member movable relative to said first member to indicate variations in a given characteristic, a pair of thermal strips connected so that the strips constitute continuations or each other and the high expansion side of one strip constitutes a continuation of the low expansion side of the other strip, said thermal strips having the same effective length and the same configuration, a rigid support for one of said connected strips, the other end of said connected strips being free to move relative to said support, a connection between the free end of said connected strips and one of said members, and means for variably heating one of said strips.

5. In a device of the class described, the combination of a pair of arcuate thermal strips each having a high expansion side and a low expansion side, said strips being connected in overlapping relationship with a side oi! one strip in contact with the like side of the other strip, a rigid support for one end of said connected strips, the other end of said connected strips being tree to move relative to said support, means for variably heating one of said strips, and indicating means connected to said strips for operation thereby.

6. In a device of the class described, the combination of a pair of thermal strips each having a high expansion side and a low expansion side and connected in overlapping relationship with a side of one strip in contact with the like side of the other strip, a rigid support for one end of said connected strips, the other end of said connected strips being free to move relative to said support, an actuating heating coil for heating one of said strips, said actuating coil being adapted for connection to a resistance variable with a given characteristic whereby the current in said coil is varied in accordance with variations in said characteristic, a voltage compensating heating coil for the other strip, and indicating means connected to said strips for actuation thereby.

7. In an indicator of the class described, the combination of a dial, a pointer movable relative to said dial to indicate variations in a given characteristic, a pair of arcuate bimetallic strips connected to each other, one of said strips having its high expansion side on the outside of its arc and the other of said strips having its high expansion side on the, inside of its arc, a rigid support for one end of said connected strips, gearing connecting the other end of said strips and said pointer, the other end of said connected strips being free to move relative to said support, and means for variably heating one of said strips.

8. In a device of the class described, the combination of a pair of thermal strips each having a high expansion side and a low expansion side and connected so that the low expansion side of one strip constitutes a continuation of the high expansion side of the other strip and the high expansion side of the first strip constitutes a continuation of the low expansion side of said other strip, a fixed support for one end of said connected strips, the other end of said connected strips being free to move relative to said support, electrical means for variably heating each of said strips, a rheostat in series with one of said electrical means,- and indicating means connected to the other end of said strips for operation thereby.

GEO. E. COXON. 

